1. Field of the Invention
This invention relates to rotating bearing systems made of amorphous metallic alloys.
2. Description of the Previously Published Art
Design of a rotating mechanical system involves a constant trade-off of materials and geometries to balance the requirements of energy available versus static, dynamic, and friction loads.
Ball bearings provide the best friction performance because the device is operating in the regime of rolling versus sliding friction. However, the tangential points of the balls on a shaft represent stress concentrations because the load on the ball is distributed over a very small area; specifically, the tangential point of the ball which comes in contact with the bearing race. Depending on the particular material, the stress concentration can evolve into grooved races, grooved shafts, and flattening of the balls. These phenomena in turn lead to corrosion, spalling, galling and eventual failure of the bearing. Moreover, a tight tolerance., well matched and balanced ball bearing is difficult to manufacture, and in some cases requires hand selection of the constituent balls.
Journal bearings, on the other hand, provide a large area for load distribution which overcomes the grooving, spalling and flattening problems associated with ball bearings. However, a journal bearing operates in the regime of sliding friction which results in more mechanical losses than rolling friction due to the higher contact area. Lubrication will, of course, minimize the friction issues, within some limits such as viscosity, load density, and surface clearance, but this requires care to ensure that the journal surfaces remain clean and well lubricated. Improper lubrication or decreased cleanliness of the mating surfaces of a journal bearing creates a potential for catastrophic bearing failure due to heat build-up. Consequently, a material that possesses an intrinsically low coefficient of friction, on the order of a ball bearing, and the strength of a journal bearing, and requires no lubrication, would represent a significant engineering advance.
Journal bearing surfaces made of amorphous alloys are briefly described in terms of composition in U.S. Pat. No. 4,555,186 to D. M. Scruggs. The journal bearings in this patent are for use under heavy loads in rolling cone rock bits. The lower load bearing engaging surfaces of the main and secondary journal bearing areas of the mounting pin and the thrust loaded bearing surfaces of the pin are coated with or have attached thereto a layer of an amorphous metal. The amorphous compositions listed have the predominant constituents being W, Nb, Co, Re, Ru, Fe and Mo with a crystallization temperature above 600.degree. C. The bearings made of this material require lubrication. These amorphous compositions listed do not contain zirconium and there is no recognition of any possibility of molding the materials due to any plastic flow properties at temperature lower than the 600.degree. C. crystallization temperature. The Scruggs patent fails to describe how these material can be obtained in large, bulk quantities. Although Vicker Harness Numbers are given for 13 compositions, there are no examples given to show that any large bearing structures were ever made with any of these amorphous materials.
The problem with using amorphous metals is that it is difficult to make them in large quantities so that relatively large structures such as journal bearings can be made. The common impediment to large scale production of amorphous metals is the requirement to very rapidly cool the metal during the formulation process so that it remains amorphous. Therefore, bulk production of the amorphous metals by this technique does not appear to be presently possible.
U.S. Pat. No. 4,564,396 to W. L Johnson and R. B. Schwartz describes metastable amorphous or fine crystalline materials that are formed by solid state reactions by diffusion of a metallic component into a solid compound or by diffusion of a gas into an intermediate compound. However, this approach will result in amorphous metal rods limited to 15 mm diameter. This limits the amount of material that can be molded and does not support the manufacturing process intended for this application.
3. Objects of the Invention
It is an object of this invention to provide low friction bearings surfaces.
It is a further object of this invention to provide low friction applications for amorphous metal compositions.
It is a further object of this invention to provide low friction applications for amorphous metal compositions. requiring no organic lubrication.
It is a further object of this invention to provide low friction applications having at least amorphous metal compositions on the contacting surfaces.
It is a further object of this invention to provide low friction journal bearings using amorphous metal compositions.
It is a further object of this invention to provide bearings made of an amorphous alloy having a coefficient of friction of less than 0.5 and having a tensile strength of 1.0 GPa or greater.
It is a further object of this invention to provide bearings made of an amorphous alloy having a shear modulus of at least 30 GPa and a Youngs modulus of at least 80 Gpa.
It is a further object of this invention to provide bearings made of an amorphous metal which is moldable at a plastic flow temperature which is less than the crystallization temperature.
It is a further object of this invention to provide bearings made of an amorphous alloy which is homogeneous and isotropic with no significant defects such as dislocations, inclusions, or grain boundaries so as to be resistant to cracking and to failure under load.
It is a further object of this invention to provide a significant decrease in manufacturing complexity of bearings due to the ability of this material to be injection moldable without loss of performance.
It is a further object of this invention to provide a method to make an article of an amorphous alloy by molding or forming it at a temperature below its crystallization temperature.
These and further objects of the invention will become apparent as the description of the invention proceeds.